Fiber reinforced plastic structures have been commercially produced for some years, the processes for producing these structures requiring the incorporation of a reinforcing fiber, generally in the form of one or more layers of a woven or felted fiberglass, within a resin, or other fluent plastic material. This is generally done by either a wet or dry fiber lay up technique. In accordance with the former process, the resin "wetted" fiber reinforcement is laid up on a mold, and in the latter the fiber reinforcement is laid up dry on a mold, or form which serves as a mold (albeit the form may be incorporated as part and parcel of the finished product), and the fiber sprayed, brushed or otherwise coated or "wet" with the resin. The resin is then cured to form the fiber reinforced plastic structure.
Vacuum assisted, or vacuum bag techniques have been used in the past to form fiber reinforced plastic structures. In a vacuum bag technique, a flexible sheet, liner, or bag is used to cover a single cavity mold which contains the dry or wet fiber lay up. In accordance with the former, the edges of the flexible sheet are clamped against the mold to form an envelope and seal the member, a catalyzed liquid plastic or resin is generally introduced into the envelope, or bag interior, to wet the fiber, and a vacuum is applied to the bag interior via a vacuum line to collapse the flexible sheet against the fiber and surface of the mold, while the plastic wetted fiber is pressed and cured to form the fiber reinforced plastic structure. Resin fumes from the process are prevented from escaping into the ambient work space.
British Pat. No. 944,955 to Phillip Richard Green, published 12/18/63, describes a vacuum bag technique for the production of a fiber reinforced plastic structure. In accordance therewith, a plurality of layers of a dry glass fabric, or cloth, are laid upon a single cavity mold, the mold is covered by a flexible sheet, or bag, and the outer edges of the sheet are sealed upon the mold to leave an internal mold space in which the dry lay up is contained. A liquid resin is introduced via a supply line located at the top center of the bag to the bag interior, or mold space, to cover the dry lay up, and a vacuum is drawn upon the bag via a vacuum line located at a peripheral edge of the mold. The bag is collapsed against the mold, to press and force the fiber to follow its contour, and heat may be applied to cure the resin. The Patentee suggests the "In the case of some resin materials of high viscosity, it may be necessary to assist the flow of resin through the mold space by applying a suitable squeegee or roller to the outside of the bag." In producing satisfactory fiber reinforced plastic structures, particularly structures of maximum strength, it is recognized that islands formed by either too much or too little plastic, especially dry sports, must be avoided. All of the fiber should be wetted by the plastic, but such laminate should contain only sufficient resin to bond the fibers. The finished fiber reinforced plastic structure must be homogenous.
In U.S. Pat. No. 4,312,829, which issued to Frederic J. Fourcher on 01/26/82, there is also described a mold section and a second (upper) flexible mold section, the edges of the flexible mold section of which are sealed and supported upon the rigid mold section to leave an internal chamber. The upper side of the flexible mold section is provided with an inlet through which a resin can be introduced to the chamber, and a vacuum outlet for pulling a vacuum upon the chamber. A perforated core material is placed within the chamber to which the resin is introduced, and on which the resin is set for formation of a resin-core structure. A matting can be placed atop the core to prevent escape of resin into the vacuum outlet. After the plastic has set, the flexible, or upper mold is removed.
U.S. Pat. No. 2,913,036, issued on 11/17/59 to George H. Smith, describes a vacuum bag method wherein a rigid network of veins or arteries are extended upwardly from the base of the mold. The purpose of the veins or arteries is to flow the plastic, or resin, upwardly through the mold surface to apply at a multiplicity of points a fluid plastic, or resin, which may then seep from the points to every part of the mold space. The veins or arteries are elongated, generally rigid members coated with a permeable material, or embedded between layers of the fabric reinforcing material to become an integral part of the final casting, appearing therein as reinforcing ribs. If the veins or arteries are not to be embedded in the final product, it is suggested by the Patentee that they be left uncovered or only lightly covered upon the outside of the fabric. Then, after the casting is hardened, the artery structure can be broken away from the finished fiber plastic structure, and discarded. If true, as suggested by the Patentee, that the resin can be distributed to provide "a good, void-free, homogenous laminate" the necessity of having to incorporate the network of veins or arteries in the fiber plastic structure can lessen or even destroy the value of many products. Or, the alternative, of having to break the veins and arteries free of the finished fiber plastic structure is extremely burdensome, and can injure the surface characteristics of the product. Moreover, albeit better distribution of the resin may be possible than conventional at the time, the fact that the resin introduced into the vacuum bag must be drawn straight up against gravity, and then vertically and radially against gravity within the reticulated structure, leaves much to be desired in terms of producing a structure in which the distribution of resin is entirely and consistently uniform.
In U.S. Pat. No. 4,132,755 which issued on 01/02/79 to Jay Johnson there is disclosed a "bag within a bag" vacuum bag technique for obtaining better and more uniform distribution of the resin. In accordance therewith a perforated flexible sheet is placed over the dry fiber lay up within the inner chamber is a single cavity mold, and the inner chamber is connected to a vacuum source. An impervious flexible sheet is placed over the perforated flexible sheet to provide an outer chamber between the two sheets, the outer chamber is connected to a resin source, and the edges of both sheets are sealed upon the mold surface. In accordance with this method better distribution of the resin throughout the mold space is obtained than with that of Smith because, in the words of the Patentee, "the resin, instead of flowing longitudinally through the glass fibers and giving a `washing` effect which orients these fibers is evenly distributed through the many pinhole-like apertures in the perforated sheet. In this manner each drop of resin reaches every corner of the laminate without flowing lengthwise through the glass reinforcement." Albeit it can be said that Johnson's "bag within a bag" technique may provide more uniform distribution of the resin, and provides better resin-to-reinforcement ratios, this technique to is not without its limitations which appear to severely restrict its use. It has thus been found, e.g., that the paths of distribution of the resin across the upper surface of the impervious flexible sheet within the outer chamber results in considerable channeling, is considerably lacking in establishing a uniform network of flow paths, and flow through many of the pinhole-like apertures is far from uniform. Often large areas of the inside face of the impervious sheet collapses against the outer face of the perforated sheet and the flow of resin through these areas greatly restricted, or as most often happens interrupted altogether. Whereas massaging the surfaces from the outside, as suggested by Johnson, can sometimes help in alleviating this condition by reinitiating or increasing the rate of flow of resin through these areas, constant attention by an operative is required. Without this type of constant assistance, it is not possible to operate on a continuous basis. Thus, there remains a pressing need for a process, or apparatus, or both, for adequately uniformly distributing resin to a fiber lay up as is required for constructing superior, or even acceptable fiber reinforced plastic structures. There also is a pressing need for a process, and apparatus, of this type which will require minimum use of operating labor.